The top safety expert for a national skydiving association said a “mini-tornado,” known to jumpers as a dust devil, caused the Calverton accident Wednesday that killed a correction officer and injured his instructor during a tandem jump.

The mix of wind and dust churned into a funnel and made it impossible to control the parachute, said Rich Winstock, a national director of the United States Parachute Association, who chairs the organization’s safety and training committee. Witnesses told Riverhead police Wednesday that the parachute had opened before the victims hit the ground.

Gary Messina, 25, a New York City correction officer who grew up in Medford, was killed, and his instructor Christopher Scott, 28, was critically injured in the 4:10 p.m. accident at Calverton-based Skydive Long Island.